but the analogy is very considerable. However, greater significance should 

 be attributed to the very fact of the shedding of the part of the disc or the 

 cercomere caused by the changes of adaptive peculiarities in the process of 

 individual development. Only after the establishment of the fact of the au- 

 totomy of the part of the disc in Mircocotylidae do reasons for the shedding 

 of the cercomere of tapeworms, which appears at first a very strange phe- 

 nomenon, become clear. Actually in Microcotylidae it is connpletely clear 

 that the posterior (the first) edge hooks and both pairs of middle hooks, 

 which play a leading role in the attachment of the larva during the develop- 

 ment of more powerful attaching organs --clamps, lose their functional 

 significance and are either retained as a remnant known to be inactive for 

 the entire life or are completely cast off. Likewise, it is not less under- 

 standable that this process embraces only one pair of edge hooks and par- 

 ticularly the one lying between the middle hooks. As we have seen above, 

 the reason for this is that only this pair is used in the formation of clamps. 

 It is connpletely understandable that with the oligomerization of edge hooks 

 characteristic for the general line of development of the edge hook apparatus 

 and with the loss of their function autotomy of the section of the body-- 

 cercomere, which bears these non-functional remnants, takes place. At the same 

 time, as is usually characteristic for many rudimentary formations, the 

 interruption of the normal process is often observed for instance the 

 retention of hooks in the body and the rejection of only a part of the cercomere 

 deprived of the latter. All this is understandable, and one can only join the 

 opinion of V. A. Dogiel that it is "one of the most significant discoveries 

 in the domain of embryology of worms during the last two decades" (Dogiel, 

 1954a). 



Among the data obtained during recent years on the structure of 

 monogenetic trematodes,a large number appear to be important from the 

 point of view which interests us. Thus, the discovery of the special sub- 

 family of Diplectanidae--Rhamnocercinae (see page 355) showed the obvious 

 error in the objections of Fuhrmann (Fuhrmann, 1928-1932) concerning the 

 fact that the presence of complex cuticular thorns with their points directed 

 forward contradicts the point of view about recognizing as the posterior end p. 475 

 of Gyrocotylidae the end which bears the rosette as (because it is a structure 

 which is not encountered, nobis) the one which is never encountered anyv>/here else 

 in the animal kingdom. However, we have already written about the "scales" 

 of Diplectaninae. whose points face forward. An interesting example is cited 

 by V, N. Beklemishev in the second edition of his work (Beklimishev, 1950); 

 "in the larvae of the mosquito Aedes , swimming forward by means of their 

 heads, the microsetae of the anterior part are oriented forward whereas the 

 microsetae of the posterior part of the body--backward. . . " "Thus, " writes 

 Beklemishev, "the direction of the angle of inclination of the skin thorns is 

 an adaptive characteristic, depending on the direction of the movement of 

 the animal and not possessing significant constancy to serve as a criterion 

 of the anterior end of the body from a morphological point of view. " How- 

 ever, the example of Rhamnocercinae is interesting also from another point 



568 



